Molarity Calculator Online Free Tool
Molarity Calculator
Calculator Inputs
Molarity Formula
M = m / (MW × V)
Molarity = Mass / (Molecular Weight × Volume)
Calculation Results
0.0000 g
0.0000 mg
0.0000 g/mol
Molar mass of compound
0.0000 L
0.0000 mL
0.0000 M
0.0000 M
Solution Details
0.000000 mol
0.0000 M
0.0000 mM
0.0000 μM
0.0000 g/L
0.0000 mg/L
0.0000 kg/m³
0.0000 mol/m³
0.0000 g/L
Interactive Visualizations
Shows how concentration changes with serial dilutions of your solution
Understanding Concentration Units
Molar Concentration Units
M (Molar)
Moles of solute per liter of solution
mM, μM, nM
Millimolar, micromolar, nanomolar (10⁻³, 10⁻⁶, 10⁻⁹ M)
mol/m³
SI unit: 1 M = 1000 mol/m³
Mass Concentration Units
g/L, mg/L, kg/L
Mass of solute per volume of solution
ppm (parts per million)
Equivalent to mg/L for dilute aqueous solutions
ppb (parts per billion)
Equivalent to μg/L (1000× more dilute than ppm)
kg/m³, g/m³
SI units: kg/m³ = g/L, g/m³ = mg/L
Note: Mass concentration units (g/L, ppm, etc.) require molecular weight for conversion to molarity. The calculator automatically handles these conversions based on your selected units.
Common Laboratory Solutions
Physiological Saline
0.9% NaCl
0.154 M
154 mM
Blood Glucose
~90 mg/dL
0.005 M
5 mM
Lab HCl Solution
Standard acid
1 M
1000 mM
Concentrated HCl
37% solution
12 M
12000 mM
Dilute NaOH
Weak base
0.1 M
100 mM
Understanding Molarity
Master the fundamentals of solution concentration and molarity calculations
What is Molarity?
Molarity (M) is the most common unit for expressing solution concentration in chemistry. It represents the number of moles of solute dissolved per liter of solution. This standardized measurement allows chemists to precisely describe and reproduce solution compositions across laboratories worldwide.
The Molarity Formula
M = n / V
or when using mass:
M = m / (MW × V)
M = Molarity (mol/L)
n = Number of moles (mol)
m = Mass of solute (g)
MW = Molecular weight (g/mol)
V = Volume of solution (L)
Key Characteristics:
- Temperature-dependent: Volume changes with temperature, affecting molarity
- Easy to measure: Based on volume, which is simple to measure accurately
- Stoichiometry-friendly: Directly relates to chemical equations
- Universal standard: Recognized and used globally in scientific research
Practical Examples
Example 1: Making a NaCl Solution
You need to prepare 500 mL of a 0.5 M sodium chloride (NaCl) solution. Molecular weight of NaCl = 58.44 g/mol.
m = M × MW × V
m = 0.5 M × 58.44 g/mol × 0.5 L
m = 14.61 grams
Solution: Weigh 14.61 g of NaCl, dissolve in water, and dilute to exactly 500 mL total volume.
Example 2: Dilution Calculation
You have a 2 M HCl stock solution and need 250 mL of 0.1 M HCl for an experiment.
C₁V₁ = C₂V₂
2 M × V₁ = 0.1 M × 250 mL
V₁ = 12.5 mL
Solution: Add 12.5 mL of 2 M HCl to a flask, then dilute with water to 250 mL total volume.
Example 3: Concentration from Mass
A solution contains 25 g of glucose (C₆H₁₂O₆, MW = 180.16 g/mol) in 2 liters of solution.
M = m / (MW × V)
M = 25 g / (180.16 g/mol × 2 L)
M = 0.0694 M or 69.4 mM
Key Concepts & Definitions
The Mole
A mole is Avogadro's number (6.022 × 10²³) of particles. It's the SI unit for amount of substance, connecting the microscopic world of atoms to measurable quantities.
Molecular Weight
Also called molar mass, it's the mass of one mole of a substance (g/mol). Found by summing atomic weights of all atoms in the molecular formula.
Solution vs. Solvent
The solvent (usually water) dissolves the solute to form a solution. Molarity measures the final solution volume, not the solvent volume alone.
Dilution Factor
The ratio of initial to final concentration. A 1:10 dilution means mixing 1 part solution with 9 parts solvent, reducing concentration by 10-fold.
Stock Solutions
Concentrated solutions stored for later dilution. They save storage space and allow flexible working concentrations through dilution as needed.
Serial Dilution
A stepwise dilution series where each step dilutes the previous solution. Used to create very dilute solutions or concentration gradients.
Laboratory Applications
Research & Industry Uses
Analytical Chemistry
Titrations, standard solutions, and calibration curves all depend on precise molar concentrations. Analytical methods require accurate molarity for quantitative analysis.
Biochemistry & Molecular Biology
Buffer solutions, enzyme assays, and cell culture media require specific molar concentrations. Biological systems are sensitive to even small concentration changes.
Pharmaceutical Manufacturing
Drug formulations specify active ingredients in molar terms. Quality control relies on precise concentration measurements to ensure efficacy and safety.
Environmental Science
Water quality testing measures pollutants and nutrients in molar or mass concentrations (ppm, ppb). Regulatory limits often specify maximum allowable concentrations.
Chemical Synthesis
Stoichiometric calculations require knowing reactant concentrations. Reaction yields and kinetics depend on precise molar ratios of reagents.
Practical Preparation Tips
Calculate Required Mass
Use the formula m = M × MW × V to determine how much solute to weigh. Always double-check your calculations before proceeding.
Use Proper Glassware
Volumetric flasks provide the most accurate final volumes. Graduated cylinders are less precise but acceptable for less critical applications.
Dissolve Before Diluting
Add solute to less than the final volume, ensure complete dissolution, then dilute to the mark. Never add solvent first then solute.
Mix Thoroughly
Invert volumetric flasks 10-15 times or stir solutions completely. Incomplete mixing leads to concentration gradients and inaccurate experiments.
Label Properly
Include chemical name, concentration, date, and initials. Clear labeling prevents dangerous mix-ups and ensures traceability.
Common Mistakes to Avoid
Calculation Errors
Confusing Volume Units
Always convert mL to L before calculating. Using mL directly gives results 1000× too high.
Wrong Molecular Weight
Using atomic weight instead of molecular weight for compounds. NaCl is 58.44 g/mol, not 23 g/mol.
Forgetting Hydration
Many salts contain water of hydration. CuSO₄·5H₂O weighs more than anhydrous CuSO₄.
Dilution Formula Misuse
C₁V₁ = C₂V₂ gives the volume of stock solution needed, not the volume of solvent to add.
Preparation Errors
Adding Solvent to Full Mark First
The dissolved solute increases total volume. Always dissolve first, then dilute to mark.
Temperature Ignorance
Solutions prepared at different temperatures have different concentrations. Standardize to 20-25°C.
Using Contaminated Chemicals
Impure reagents give incorrect concentrations. Always use appropriate grade chemicals for your application.
Poor Storage Practices
Solutions degrade over time. Some require refrigeration, darkness, or inert atmosphere to maintain concentration.
Best Practice: Always verify calculations with a colleague, use calibrated equipment, and maintain detailed preparation records. When in doubt, prepare fresh solutions rather than risk using degraded or contaminated stock.
Key Takeaways & Best Practices
Essential Principles
Molarity is volume-dependent: Always measure final solution volume, not just solvent volume. Temperature affects volume and thus molarity.
Molecular weight matters: Converting between mass and molar concentrations requires accurate molecular weights from reliable sources.
Dilution is multiplicative: Each dilution step multiplies concentration by the dilution factor. Serial dilutions compound these factors.
Precision varies with application: Analytical work demands higher precision than routine preparations. Match your accuracy to your needs.
Your Next Steps
Practice calculations with the calculator above using real examples from your work or studies.
Create a reference sheet with molecular weights of commonly used chemicals in your lab.
Verify your solution preparations by remeasuring concentration with analytical methods when possible.
Establish standard operating procedures for solution preparation in your laboratory.
Master Solution Preparation
Understanding molarity is fundamental to all laboratory work in chemistry, biology, and related sciences. Whether you're preparing buffers for biochemistry, titrating solutions for analysis, or formulating pharmaceutical compounds, accurate molarity calculations ensure reproducible results and safe practices. Use this calculator regularly to verify your work, explore different scenarios, and build confidence in your solution preparation skills. Remember that precision in preparation leads to reliability in results.